SC Brake Pedal "Feel"

[Halm]

I have a question about my SC’s brake pedal “feel” that I didn’t see when I was searching the archives, so I will throw it out for comments.

I have a 993 as well as my SC. The brakes in the 993 are fantastic. The pedal is rock solid and it doesn’t seem to move when applying the brakes. It is almost like there is a sensor that is measuring the amount of force and the car brakes accordingly. The SC, on the other hand, has significant (relatively speaking) travel. It stops great and has never remotely given me concern when on-track at a DE.

Over the last two years I have done the following things as wear and tear have required: rebuilt rear calipers, stainless steel brake lines, new master cylinder, new front rotors, rebuilt front calipers, and new brake pads. And I flush the ATE Super Blue several times per year for each DE. Even with all of this the pedal still has a lot of movement.

My question then, is this simply the way SC brakes feel? Am I dealing with the contrast between two entirely different brake systems, apples and oranges? Is there anything else I can try short of upgrading the brakes to move the feel toward that of the 993? Motul or Castrol SRF make any difference?

[jimrs2000]

Halm,

Mine is the same, I have checked the braking system out and it is fine so I have just assumed thats the way it is, significant travel but no problems stopping the car.

This is my first 911 but I have a lot of experience with race and rally cars from the same late 70's and early 80's, most of which are the same.

I think that as cars have developed we have got used to power everything and the power assist on brakes and steering particularly has been turned up so a lot of the "feel" has gone away.

Personally I like the feel of the brakes as you can tell how much grip you have and when you are about to lock a wheel.

just my 10 cents...

[Oh Haha]

My SC is the same way. Again, the brake system has been rebuilt and works fine.

Oddly, my Mazda gives me more confidence when faced with certain situations. I drive it daily so the comparison is probably not realistic.

[Bill Verburg]

You can change pedal feel by changing to a larger m/c. An '80SC uses a 20.64mm m/c stock. The only one I know of that is bigger is a 930 23.8mm which in MO is too big, but some guys do use them and seem to be ok w/ it.

stock your slave/master ratio is 35.192 w/ a 23.8 it goes to 26.5. The lowest unboosted ratio I've ever used is ~32.3, those brakes needed a lot of leg, the lowest boosted factory ratio is ~30. These low ratios are only used on the RS and/race cars, the absoulute lowest is ~29.5 unboosted on the late Cup & RSRs w/ twin m/c

A nice compromise if you can find one that fits is ~21-22mm

[Eric_Shea]

Couple of things Gents,

1. There's a difference between the two systems; that's for sure. Kind of like jumping out of my Pig (aka: Cayenne) and into my early 911. The SC system is virtually identical in all fluid dynamics to the early 911 (19mm MC, 48mm pistons up front, 38mm pistons in the rears, etc.) That said, you should be able to get a higher pedal etc.

2. If you've recently rebuilt your calipers your seals may need to be broken in. New seals will pull the piston back further than those that have been bedded in properly. Did you bed your pads properly? There's a procedure on my site you should follow regardless of pad brand etc. This (seal) dilema is outlined in the factory manuals. Bed your pads and it will help bed your seals in... you pedal will come up.

3. Is the plunger on your pedal assembly set properly? This is outlined in all the manuals as well but, a lot of people don't check or adjust this.

4. A-Calipers - These are some of the first ATE calipers without the "Knockback Mechanism". If you look at your pistons and compare them to Earlier M-Caliper or S-Caliper pistons you will noticed they are shaped like a cup. The calipers no longer have the pin in the center and the pistons (obviously) no longer have the self ratchetting knockback mechanism. This device was designed to keep a high pedal by keeping the piston/pad as close to the rotor as possible. Also, these cars do not come with a secondary pressure valve to keep pressure on the system (more common in newer cars).

So... combine the above and you may see why your pedal isn't exactly where you think it should be. Hope that helps but, keep in mind technologies change. I don't expect my early 911 to feel like my Cayenne. Ones a fox and one's a pig.

[Bill Verburg]

Originally Posted by Eric_Shea

Couple of things Gents,

1. There's a difference between the two systems; that's for sure. Kind of like jumping out of my Pig (aka: Cayenne) and into my early 911. The SC system is virtually identical in all fluid dynamics to the early 911 (19mm MC, 48mm pistons up front, 38mm pistons in the rears, etc.) That said, you should be able to get a higher pedal etc.

2. If you've recently rebuilt your calipers your seals may need to be broken in. New seals will pull the piston back further than those that have been bedded in properly. Did you bed your pads properly? There's a procedure on my site you should follow regardless of pad brand etc. This (seal) dilema is outlined in the factory manuals. Bed your pads and it will help bed your seals in... you pedal will come up.

3. Is the plunger on your pedal assembly set properly? This is outlined in all the manuals as well but, a lot of people don't check or adjust this.

4. A-Calipers - These are some of the first ATE calipers without the "Knockback Mechanism". If you look at your pistons and compare them to Earlier M-Caliper or S-Caliper pistons you will noticed they are shaped like a cup. The calipers no longer have the pin in the center and the pistons (obviously) no longer have the self ratchetting knockback mechanism. This device was designed to keep a high pedal by keeping the piston/pad as close to the rotor as possible. Also, these cars do not come with a secondary pressure valve to keep pressure on the system (more common in newer cars).

So... combine the above and you may see why your pedal isn't exactly where you think it should be. Hope that helps but, keep in mind technologies change. I don't expect my early 911 to feel like my Cayenne. Ones a fox and one's a pig.

911 unboosted w/ A or S and M and 19mm m/c have a higher slave/master ratio than later boosted sytems w/ the 20.6.
w/ 19mm it's 41.3
w/20.6mm it's 35.192

the higher the ratio the more pedal travel

[Bill Verburg]

Ate does make 22.2mm boosted tandem m/c that might work, i've never fitted one but
ATE#
03.2122-0142.3
03.2122-6912.3
03.2122-9612.3

these are all 22.2mm that might work

[Halm]

Great info everyone. Thanks! And Bill, if I can find one of the ATE m/c's you list, I'll let you know how it works out.